The present invention relates to the casting of metal alloys with low melting temperatures, and more specifically to a nozzle for providing an interface connection from a transfer line to a die.
Low temperature melt out metal parts of complex shapes are made for use as cores in subsequently molded plastic components, and other embodiments, metal alloys with low melting temperatures are used for encapsulating components, such as turbine blades, so they may be held for machining and other finishing steps. After use, the metal from the cores or encapsulations is remelted and reused.
To ensure that a uniform density and fine grain structure for castings and encapsulations is achieved, it is necessary to cast the material under low pressures quite different from that of a die casting process. Metal alloys with low melting temperatures cannot be used in the die casting process. Air holes and cavities are formed in these alloys when die cast and this results in imperfect castings being produced. In die casting, shot pressures are generally in the range of 800 to 4,000 lbs per sq. inch and the time for injection is in the order of 30 to 40 milliseconds. In such an operation where hot metals are injected at a high velocity and with turbulent flow into a die through a narrow gate, air can become entrapped and pressures build up in the cylinder and passage to the die. These high speed injection processors generally include runners leading into the die, and the unsolidified metal drains back after the casting process.
Melt out metal parts are made wherein the melting temperature of the metal alloys is generally below 350.degree. C. High pressure die casting is not appropriate for making melt out metal parts or encapsulations because the desired dimension tolerances cannot be achieved. Castings of melt out metal alloys are generally produced by allowing liquid metal alloy to flow into a die under substantially no pressure. After the die is full, a small pressure, generally in the order of 30 to 50 lbs per sq. inch is built up in the die during the cooling stage. The filling and cooling time can vary from about 3 to 30 seconds depending upon the size of the casting.
One example of an apparatus for casting metal alloys with low melting temperatures is disclosed in U.S. patent application Ser. No. 268,492 filed Nov. 8, 1988. An improved valve mechanism for casting metal alloys with low melting temperatures is also disclosed in U.S. application Ser. No. 520,213 filed May 7, 1990.
Liquid metal alloy flows from a cylinder in a liquid metal alloy tank, through a transfer line outside the tank, and into a die through a nozzle which interfaces with the die. After the casting, the die is removed from the nozzle, cooled and then opened to remove the casting. In certain types of casting machines, where multiple injection points are required on the die or dies, a manifold is supplied with a number of nozzles on the manifold fed from a single supply source of liquid metal alloy. Difficulties can occur due to nozzles or dies having slightly different dimensions. This can result in liquid metal alloy spillage at the interface between the nozzle and the die. Another problem that can exist is misalignment between the die and the nozzle and this too can result in spillage of liquid metal alloy.
A further problem that can exist is that when the die is separated from the nozzle. Frozen metal alloy sometimes extends into the nozzle which causes difficulties in separating the die from the nozzle. There is thus a need to resolve these problems.